1. Field of the Invention
Exemplary embodiments of the present invention relate to performing diagnostics on an integrated circuit and, more particularly, to obtaining real-time trace information on programs being executed by multiple processors fabricated on integrated circuits.
2. Description of Background
Tracing instruction or program execution flow is helpful in debugging, or locating causes of problems in software programs being executed by a processor. The term tracing generally refers to process of logging occurrences of specific events during instruction execution. More particularly, the tracing of instruction fetches allows for a captured history of code that has been executed to be obtained. From this information, a determination can be made of steps taken during the program execution to reach the present instruction and state of operation. This is often helpful and sometimes necessary to remove programming errors and to diagnose common problems. In on-line or real-time tracing systems, the target program and the other programs run concurrently, and the data is conveyed between them during instruction execution.
In computer architecture, the combination of a processor (or more than one processor in multiprocessor systems) and main memory (that is, memory that the processor can read and write to directly, with individual instructions) is generally considered to be the heart of a computer. Real-time trace information of program operations executed by a processor can be obtained using the trace function of the processor. For example, the processor may have a physical, dedicated I/O for outputting trace information so that state of the processor can be monitored from outside. In other situations in which the processor has no dedicated I/O for tracing, the operating information of the processor can be output through its General Purpose Input/Output (GPIO) ports.
The term system-on-a-chip (SoC) is used to refer to a single integrated circuit or chip that includes all the components of a computer or other electronic system. As a result of continued advancements in the very-large-scale integration (VLSI) process, more and more circuitry is able to be integrated onto each chip. Thus, the number of processors that can be integrated on a single SoC has been increasing, and it is foreseeable that a single SoC chip may integrate 16 to 128 or more processors in the future. Currently, to obtain real-time operation information for all the processors on such a chip, a separate peripheral I/O channel for tracing each of the integrated processors would be required. For instance, an SoC integrating 128 processors would require 128 peripheral I/O channels for tracing. Because of bandwidth limitations, however, such a large number of peripheral I/O channels are not practical. Furthermore, because the amount of hardware required for a circuit to perform tracing increases as the number of processors increases, it is desirable to implement simpler circuitry for performing tracing.
The number of the peripheral I/O channels available for obtaining trace information on an SoC is also limited by the availability of bus connector placement and issues raised by specific wiring regions on the board, as well as the manufacturing cost. As the parameters of these limitations do not typically manifest until the board is actually being designed and manufactured, the number of peripheral I/O channels that will be available for tracing is hard to estimate prior to designing the SoC. For example, assuming there is an SoC having four processors and four sets of peripheral I/O channels available for tracing, if only one bus connector for tracing can be placed on the board, only one of the four processors can be connected to the bus to provide tracing information. As a result, the trace of the remaining three processors cannot be obtained. Thus, it is desirable to provide for flexibility in connector placement and wiring of the peripheral I/O channels available for tracing on an SoC at the time the board is manufactured to enable trace information on all the processors on the SoC to be obtained.
First Silicon Solutions Ltd. (FS2) has developed a system called Multi-Core Embedded Debug (MED) for performing tracing in multi-core chips. This system provides for a debugging bus in a chip so that information required for debugging can be propagated on the bus for storage in a trace buffer. In particular, the trace information from the processors on the chip is placed on the debugging bus and recorded in the trace buffer. Because the system relies on the connections between this bus and the trace output from each of the processors on the chip, the number of connections that must be made with the bus to obtain trace information for all the processors increases with the number of processors on the chip. If an independent connection to the bus cannot be provided for each processor, more than one processor will compete for a single bus, and only one processor can get the bus grant at a time. This causes the load on the bus to increase, which in turn lowers the operating frequency of the system. That is, even as the number of processors on the chip increases, it becomes difficult to increase the operating frequency of the tracing mechanism. Furthermore, if the number of processors in the design of the chip changes, a corresponding change in the design of the arbitration logic for the bus connections is required, and this has the effect of decreasing the modularity of the system. Accordingly, it is difficult to implement a scalable design in such a system that enables high-speed operation equivalent to the operating frequency of the processor.